Abstract: A system to dehumidify a substantially sealed chamber (2) which includes a recirculating duct (1) which recirculates air within the chamber. The duct includes an exchange aperture (3) facing the direction of flow of air (4). A fan (5) to draw air through the duct is positioned downstream of the exchange aperture. A heater (19) is provided preferably within the recirculating duct and preferably located downstream of the display aperture. The sealed chamber (2) may be a spray painting booth for painting vehicles.